Add utility classes (Slice, Fd, Status, etc)

Test: as follows
    - built
    - flashed
    - bootedt log
    - netdutils_test passes
    - unsubmitted NFLogListenerTest passes
Bug: 28806131

Change-Id: I17846a0dee1edca55df10e5464e607109d978cb5
diff --git a/libnetdutils/Slice.cpp b/libnetdutils/Slice.cpp
new file mode 100644
index 0000000..7a07d47
--- /dev/null
+++ b/libnetdutils/Slice.cpp
@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <sstream>
+
+#include "netdutils/Slice.h"
+
+namespace android {
+namespace netdutils {
+namespace {
+
+// Convert one byte to a two character hexadecimal string
+const std::string toHex(uint8_t byte) {
+    const std::array<char, 16> kLookup = {
+        {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'}};
+    return {kLookup[byte >> 4], kLookup[byte & 0xf]};
+}
+
+}  // namespace
+
+std::string toString(const Slice s) {
+    return std::string(reinterpret_cast<char*>(s.base()), s.size());
+}
+
+std::string toHex(const Slice s, int wrap) {
+    Slice tail = s;
+    int count = 0;
+    std::stringstream ss;
+    while (!tail.empty()) {
+        uint8_t byte = 0;
+        extract(tail, byte);
+        ss << toHex(byte);
+        if ((++count % wrap) == 0) {
+            ss << "\n";
+        }
+        tail = drop(tail, 1);
+    }
+    return ss.str();
+}
+
+std::ostream& operator<<(std::ostream& os, const Slice& slice) {
+    return os << std::hex << "Slice[base: " << reinterpret_cast<void*>(slice.base())
+              << ", limit: " << reinterpret_cast<void*>(slice.limit()) << ", size: 0x"
+              << slice.size() << "]" << std::dec;
+}
+
+}  // namespace netdutils
+}  // namespace android